utils.py 文件源码

def initialize_urandom():
    """
    This function and the web2py_uuid follow from the following discussion:
    `http://groups.google.com/group/web2py-developers/browse_thread/thread/7fd5789a7da3f09`

    At startup web2py compute a unique ID that identifies the machine by adding
    uuid.getnode() + int(time.time() * 1e3)

    This is a 48-bit number. It converts the number into 16 8-bit tokens.
    It uses this value to initialize the entropy source ('/dev/urandom') and to seed random.

    If os.random() is not supported, it falls back to using random and issues a warning.
    """
    node_id = uuid.getnode()
    microseconds = int(time.time() * 1e6)
    ctokens = [((node_id + microseconds) >> ((i % 6) * 8)) %
               256 for i in range(16)]
    random.seed(node_id + microseconds)
    try:
        os.urandom(1)
        have_urandom = True
        try:
            # try to add process-specific entropy
            frandom = open('/dev/urandom', 'wb')
            try:
                if python_version == 2:
                    frandom.write(''.join(chr(t) for t in ctokens)) # python 2
                else:
                    frandom.write(bytes([]).join(bytes([t]) for t in ctokens)) # python 3
            finally:
                frandom.close()
        except IOError:
            # works anyway
            pass
    except NotImplementedError:
        have_urandom = False
        logger.warning(
            """Cryptographically secure session management is not possible on your system because
your system does not provide a cryptographically secure entropy source.
This is not specific to web2py; consider deploying on a different operating system.""")
    if python_version == 2:
        packed = ''.join(chr(x) for x in ctokens) # python 2
    else:
        packed = bytes([]).join(bytes([x]) for x in ctokens) # python 3
    unpacked_ctokens = _struct_2_long_long.unpack(packed)
    return unpacked_ctokens, have_urandom